The pumping and processing of blood has been routinely performed with patients as a means of processing their own blood or blood taken from another person and administered to the patient. Blood processing can be performed to remove a variety of blood constituents for therapeutic purposes. Hemodialysis is a widely used processing methodology that removes metabolic waste products from the blood of patients suffering from inadequate kidney function. Blood flowing from the patient travels across membranes which remove these waste products. The processed blood is then returned to the patient. Plasmapheresis similarly processes blood using tangential flow membrane separation to remove blood plasma constituents, such as cholesterol, to treat a wide variety of disease states. Membrane pore sizes are selected to remove the unwanted plasma constituents in a tangential or cross-flow separator. Hemoconcentrators use membranes with very small pores or non-porous membranes which permit water diffusion, to remove water or fluid with electrolytes from blood that is too dilute. Blood may similarly be processed in a device which utilizes biochemical reactions to modify biological constituents present in blood as a treatment for certain diseases. For example, enzymes can be bonded to membrane surfaces or gel immobilized and blood components such as bilirubin or phenols can be gluconized or sulfated by the in vitro circulation of blood plasma across these bonded enzyme surfaces. Blood is routinely processed by the addition of an anticoagulant to prevent its clotting while it is outside the body.
Blood may be processed during surgery to permit blood flowing from a wound or incision to be reinfused into the patient. This is called intraoperative autotransfusion. Such processing may include anti-coagulation and the removal of particles (debris from the wound site and clots) larger than red cells. This processing may include the removal of blood plasma and damaged blood tissue components (i.e., free plasma hemoglobin) and anticoagulant, with or without the addition of a saline washing fluid to aid in plasma removal and to replace some of the lost fluid.
Techniques and apparatus have been available for some time for washing blood cells prior to returning them to the patient. In such techniques a centrifuge is used for separating and washing the red cells in batches and they are resuspended in a balanced salt solution before infusion into the patient. This is a relatively slow process, the apparatus is complex and expensive and expertise is needed to run the apparatus.
More recently, as set forth in U.S. Pat. No. 4,631,050, issued to Charles C. Reed and Denton A. Cooley on Dec. 23, 1986, an autotransfusion system is utilized wherein the centrifuge is replaced by an ultrafiltration module. The apparatus utilizes a receiving chamber having a semipermeable membrane at least partially bonded to its inside surface. The chamber is pressurized so as to provide a significant pressure differential across the membrane and fluid and small particles are forced out of the blood and through the membrane while the membrane holds up the red cells. Thereafter, washing solution is injected into the receiving chamber to assist in plasma removal and the blood cells, along with some of the washing fluid, are swept out of the chamber and reinfused into the patient.
The system and method of U.S. Pat. No. 4,631,050 suffer from a number of problems. One of the problems is that a thick layer of red cells is formed and is retained above the ultrafiltration membrane. This requires that a relatively high pressure be provided across the membrane to achieve any practical plasma removal rate. This limits the speed of filtration. Also, the red cells held against the membrane can be damaged when subjected to the pressure differential whereby the proportion of undamaged red cells recovered and reinfused into the patient is limited. Further, the apparatus of U.S. Pat. No. 4,631,050 utilizes roller pumps which can themselves damage red cells thus still further reducing the proportion of red cells returnable to the patient. In addition, there is no means for mixing washing fluid and blood uniformly to obtain efficient washing. Also, washing fluid is added before any ultrafiltration which requires relatively large quantities of washing fluid for plasma removal. The apparatus of U.S. Pat. No. 4,631,050 only provides for batchwise addition of washing fluid rather than continuous 354 addition of washing fluid whereby washing is not as efficient as would be desired.
In plasmapheresis membrane tangential flow separators have been utilized to remove plasma from blood as an alternative to centrifugation. U.S. Pat. No. Re. 31,688 reissued Sep. 25, 1984 to R. P. Popovich, J. W. Moncrief and G. D. Antwiler discloses one such process. Such is also reported, for example, by M. Tamura and M. Kasai in Current Practice in Therapeutic Plasmapheresis, pp. 70-77, Edited by Y. Shiokawa and N. Inoue, Excerpta Medica, Amsterdam, 1985 as well as by Z. Yamazaki, et al., pp. 78-85, same book. Such membrane tangential flow separators have not, however, been known to be useful or been used in autotransfusion wherein very different problems are encountered. In plasmapheresis one has a consistent supply of whole blood, for example, from a blood vessel, and the blood flows at a relatively constant rate. In autotransfusion the rate of blood flow varies from zero on up to many times that which occurs in plasmapheresis and can do this several times intermittently during a surgical procedure. Also, it is not whole blood which flows but rather a mixture of fluids which include traumatized blood, clots, debris, entrapped gases, saline fluids, anticoagulant fluid and the like. Tangential flow separators are generally unable to handle such a mixture and would be damaged and/or clogged if one attempted to separate such a mixture using a plasmapheresis tangential separator apparatus.
The current systems for intraoperative autotransfusion, plasmapheresis, hemoconcentration, hemodialysis, and blood processing in general suffer from a number of problems. All are complex electromechanical systems which are expensive and require a trained operator as well as much time to set up and use. The systems are manual or semiautomatic but not automatic. They are not inherently safe but require sensors and safeguards and much attention to ensure safe operation. The processing of blood often occurs at rates lower than desired. The metering and mixing of anticoagulant with blood is often inadequate, leading to insufficient anti-coagulation and clotting or excessive anti-coagulation, higher cost for the anticoagulant, and the need to remove this excess (or all anticoagulant) before returning blood to the patient. Damage to retained blood constituents or excess removal of those which are desired to be retained often occurs with these systems. It is desired to retain close to 100% of the red cells and a significant proportion of platelets for return to the patient. Present systems retain substantially less than 100% of the red cells and a very low percentage of the original platelets.
The present invention is, in some of its embodiments, intended for use in all of the blood pumping and processing applications mentioned above, and in other embodiments, intended for use in autotransfusion, and is directed to overcoming one or more of the problems of existing devices as described herein.